Aldicarb is a common soil-applied chemical pesticide which has the structure of Formula (I) below: ##STR1## The IUPAC name for this compound is 2-methyl-2(methylthio)propionaldehyde 0-methylcarbamoyloxime. Once applied to soil it is taken up into plants by the roots, where it protects the plants from certain insects for several weeks. Aldicarb is toxic to humans, so there is a continuing need for methods of testing for its presence in soil, produce, and food products.
Aldicarb lingers in soil. Its persistence in soil, and its oxidation forms in soil, are well known See, e.g., J. Smelt et al., Pestic. Sci. 9, 279 (1978). In overview, aldicarb in soil oxidizes first to the sulfoxide shown in formula (II) below, and then to the sulfone shown in formula (III) below. ##STR2##
Analytical labs test for the presence of aldicarb in a sample by converting the aldicarb entirely to the sulfone form of Formula (III). Aldicarb concentration can then be reported in "sulfone equivalents". In brief, the aldicarb is converted to the sulfone by reaction with hydrogen peroxide in acetic acid under heat; then extraction of the sulfone into a nonpolar organic solvent; and then injection of the solvent into a high performance liquid chromatography apparatus (HPLC). See generally M. Dong et al., Analysis of carbamate pesticides by LC, AEL, 14-27 (Apr. 1990). The advantage of this procedure is its accuracy. The disadvantages, however, are that HPLC equipment is expensive, HPLC equipment is difficult to use, and the total process is time-consuming. Hence, the procedure must be carried out in an analytical laboratory.
It would clearly be desirable to have a procedure which can be carried out in the field, close to the source of potential contamination, so that a rapid indication of aldicarb contamination can be provided. Hence, immunoassays for aldicarb have been developed. See R. Bushway and B. Ferguson, Determination of Atrazine, Aldicarb and Methyl-2-Benzimidazolecarbamate Residues in Food by Enzyme Immunoassay (1989)(poster presented at Pacifichem '89, Honolulu, Hi, Dec. 17-22 1989). The advantage of immunoassays are that they are quick and easy to carry out. The disadvantage of immunoassays are that they employ antibodies, and antibodies bind differently to aldicarb depending on whether it is in its unoxidized, sulfoxide, or sulfone form. The known procedures for converting aldicarb to the sulfone form, however, employ chemicals which either partially or wholly denature antibodies. Hence, there is no immunoassay procedure currently available which measures aldicarb concentration after first converting the aldicarb to sulfone.
In view of the foregoing, objects of the present invention are to provide an aldicarb assay which combines the convenience of an immunoassay, while retaining the accuracy of analytical assays which report aldicarb concentration in sulfone equivalents.